1. Field of the Invention
This invention relates to a heat-developable light-sensitive material.
2. Description of the Prior Art
A photographic process using silver halides is the most commonly used photographic process, since this process is superior to the electrophotographic process or diazo-photographic process in photographic properties such as sensitivity and gradation. However, the silver halide light-sensitive material used in this process is imagewise exposed, developed with a developer and, furthermore, subjected to several processings such as stopping, fixing, water washing and stabilizing so as to prevent the developed image from discoloring or fading and the non-developed area (which will hereinafter be referred to as "background") from blackening. Thus the photographic process using silver halides has the disadvantages that much time and labor are required for the processing, the handling of chemicals is harmful to the human body and the processing rooms and the hands and clothes of the workers are stained. Therefore, it has been very desirable to improve the photographic processing using silver halides so that the processing can be carried out under dry conditions without using solutions and the processed image is maintained stable. To this end, many efforts have been made.
A first approach is the so-called one bath developing and fixing method whereby the two operations of developing and fixing in the silver halide photographic process of the prior art are combined in one bath, as disclosed, for example, in U.S. Pat. No. 2,875,048, British Pat. No. 945,453 and German Pat. No. 1,163,142. A second approach is to conduct the wet processings in the silver halide photographic process in a dry manner, as disclosed, for example, in German Pat. No. 1,174,159 and British Pat. Nos. 943,476 and 951,644. A third approach is to use a light-sensitive element comprising a silver salt of a long chain aliphatic carboxylic acid such as silver behenate, silver saccharin or silver benzotriazole, as a main component, and a catalytic amount of silver halide as disclosed, for example, in U.S. Pat. Nos. 3,152,904, 3,457,075, 3,635,719, 3,645,739 and 3,756,829 and Canadian Pat. No, 811,677. The present invention relates to the third approach.
In heat-developable light-sensitive materials, which have hitherto been proposed, for example, a composition comprising a silver salt of a fatty acid such as silver behenate, a reducing agent and a catalytic amount of silver halide, the properties of the light-sensitive material, such as sensitivity, gamma, fog and color tone deteriorate sometimes after the passage of time due to their insufficient storability. This is a very important disadvantage for a light-sensitive material.
A light-sensitive material containing a light-sensitive silver halide obtained by reacting a halide and an organic silver salt is disclosed in U.S. Pat. No. 3,457,075, but a heat-developable light-sensitive material containing a light-sensitive silver halide thus formed in a catalytic amount provides only a low contrast image. However, a high contrast heat-developable light-sensitive material is required for the purpose of copying documents as well as making films for printing plates and, accordingly, a low contrast heat-developable light-sensitive material cannot be used for this purpose. Furthermore, the heat-developable light-sensitive material of the prior art has the disadvantage that heat fog tends to occur in the non-exposed area upon heating during developing. A previous attempt to prevent formation of this heat fog is, for example, described in U.S. Pat. No. 3,589,903, which is characterized by the use of a compound capable of releasing mercury ion. However, mercury compounds are so harmful that the production or use of a light-sensitive material containing mercury compounds in hazardous. Therefore, the technique described in U.S. Pat. No. 3,589,903 can suppress the heat fog, but, on the other hand, has the disadvantage that a high hazard is unavoidable.